The present invention relates generally to a tunnel boring machine (TBM) and other machines that are configured to drill tunnels through various ground conditions and a wide range of geology. In some environments, it is cost prohibitive to completely test the geology of the path that the tunnel will traverse.
A main beam TBM is considered an “open” machine. The main beam TBM can have a shield in a forward location but does not include shields in the rearward locations of the TBM. The main beam TBM includes a cutter head and hydraulic propel cylinders that push the cutters into the rock. The transfer of this high thrust through the rolling disc cutters create fractures in the rock causing chips to break away from the tunnel face. Gripper shoes can be provided to push on the sidewalls to react the machine's forward thrust. The gripper shoes can move along the main beam. At the end of a stroke, the rear legs of the machine are lowered, the grippers and propel cylinders are retracted. The retraction of the propel cylinders repositions the gripper assembly for the next boring cycle. The grippers are extended, the rear legs lifted, and boring begins again.
Main beam and open machine designs are usually used in hard rock and can be used in unlined tunnels. The main beam TBM may have to removed from the tunnel to install tunnel lining segments. Open machines can get inundated with debris if the condition of the terrain that is being bored becomes unstable due to a lack of shields located behind the cutter head. Shielded machines have been provided for giving additional protection for operators. However, shielded machines have a risk of getting trapped and a long single shield can get trapped just as well as the double shield design can get trapped.
One example of a shielded machine is a single shield design that can be used when sections of broken ground must be bored through. The single shield design does not include a main beam. A single shield design can include one articulation with only one way to propel the TBM, through the use of thrust cylinders against tunnel lining segments. The thrust cylinders are used to push off the latest pre-cast concrete tunnel lining segment, as installed by a segment erector. In the single shield design, tunnel boring and tunnel lining erection are sequential operations, as one boring stroke can be made, and then a subsequent lining segment must be installed.
One example of a shielded machine is a double shield TBM. A double shield TBM includes a cutter head with a first shield, a second shield, a gripper shield, and a tail shield. A double shield is typically used in environments where there is fractured rock. The Double Shield TBM and the Single Shield TBM do not include a main beam. Instead, these TBMs have only various cylinders located about the central axis of the machine to carry reactions provided by the various shields. For the double shield design, the first shield telescopes within the larger second shield when the TBM moves forward. In normal operation of the double shield mode, the gripper shoes are energized, pushing against the tunnel walls to react against the boring forces. Propel cylinders are provided about the periphery of the double shield TBM in front of the gripper shoes and near the cutter head in the front of the double shield TBM. The propel cylinders are then extended to push the cutter head support and push the cutter head forward. The rotating cutter head cuts the rock. The telescopic shield extends as the machine advances keeping everything in the machine under cover and protected from the ground surrounding it. A segment erector is fixed to the gripper shield allowing pre-cast concrete tunnel lining segments to be erected while the machine is boring at a location to the rear of the gripper shoe. If the ground becomes too weak to support the gripper shoe pressure, the machine thrust must be reacted another way. In this situation, a double shield machine can be operated in “single shield mode.” Auxiliary thrust cylinders are located in the gripper shield. The thrust cylinders are used to push off the latest pre-cast concrete tunnel lining segment. In the single shield mode, tunnel boring and tunnel lining erection are sequential operations, as one boring stroke can be made, and then a subsequent lining segment must be installed. Regardless of the operating mode, working crews remain protected within the shields.
The Double Shield TBM can include a probe drill. Due to the location of the propel cylinders about the periphery of the TBM, the probe drill is located to the rear of the gripper shoe. The probe drill can be used for probe drilling at an angle relative to the longitudinal axis of the TBM by entering the rock near the location of the gripper shoe which is set back rearwardly from the cutter head. The propel cylinders prevent the probe drill from being located closer to the front of the TBM.
Despite the current open and shielded designs, there is still a need to reduce the occurrence of a machine getting trapped in the terrain due to unexpected ground conditions causing a collapse of the tunnel. It is acknowledged that time can be of the essence when forming a tunnel. This being the case, then it would be desirable for the final tunnel lining to be set by the TBM. However, this may not be practical in highly stressed ground. The geological data suggest that squeezing ground condition can occur over extended sections of the tunnel alignment. Since this squeezing effect can have major effects on the final tunnel lining, the rock stress forces must come into a balance before the final tunnel lining can be placed. There is also a need to more efficiently pre-treat the rock in advance of the cutter head. Despite prior art attempts at TBMs, there still is a need for a TBM that is equipped to handle multiple types of ground conditions while still providing maximum speed for the TBM.